Tantalum capacitors have been widely used in fields of telecommunication, computer, automobile, household appliance, aerospace et al. Tantalum electrolytic capacitors manufactured with tantalum powder as an anode and tantalum wire as anode lead have the advantages of small volume, large electric capacity, high degree of chip type, good reliability, and long service life, and therefore can operate normally under extreme conditions under which many other capacitors (such as ceramic, aluminum sheet capacitors, etc.) cannot operate.
As to tantalum wire for anode lead of tantalum capacitors, it is required to have high chemical purity, good surface finish and precise dimensions, with its mechanical properties and electronic properties satisfying the strict demands or capacitors. For example, the specific demands on surface finish of tantalum wire are as follows, the surface has no obvious defects such as grooves, burrs, and sand holes, if observed under microscope of 60 magnification or more, and the specific requirement on electronic properties is leakage current, which the smaller the better.
With the development on electronic techniques, the requirements on the tantalum capacitors have been become increasingly strict. Tantalum capacitors have been developed, step by step, towards miniaturization, chip-type, and high capacity, with the tantalum powder used having higher and higher specific capacity. The above correspondingly restricts the sintering temperature of anode pellet of tantalum capacitors. If the sintering temperature is too high, the porosity of tantalum powder is reduced largely, and thereby decreasing the specific capacity of tantalum capacitors.
However, if conventional circular anode lead is used on low-temperature sintered tantalum capacitors, the following problems will arise, the anode lead made with circular tantalum wire has small contact area with tantalum anode pellet due to its relative small surface area, thereby leading to low contact strength and excessive leakage current of tantalum capacitor, even leading to the shedding of the tantalum wire from the anode pellet which will result the failure of the tantalum capacitor. With further development of miniaturization, of tantalum capacitors, the problem of low pullout strength of lead wire of tantalum capacitors has more and more disadvantageous effect on the electronic properties and reliability of tantalum capacitors.
Although it was suggested in the early 21th century that tantalum wire of non-circular cross section was used to replace present tantalum wire of circular cross section to solve this problem. However, until now, among the tantalum capacitor manufacturing techniques, almost all the tantalum wires are of circular cross section. The reasons are as follows, none of the manufacturers can produce special-shaped tantalum wires whose chemical purity, surface finish, mechanical properties and electronic properties can meet the requirements of tantalum capacitors, in many cases, it is the surface finish, mechanical properties and/or electronic properties cannot meet the strict requirements of tantalum capacitors.